Flow order control is the basis of automatic reaction process for most biochemical analyses. The significant function requirements of flow order control include (1) the capability to switch the flow of three to five reactants, (2) correctly following the flow order of three to five reactants, (3) the capability to define and control the flow amount of three to five reactants, and (4) the capability to minimize the mixing of any two reactants with successive flow orders during the flow order control. The flow order control of multiple reactants therefore becomes the key to the automatic biochemical analysis of microfluidic chips. In the design of microfluidic chips, flow order control belongs to the high level combinational function that often requires a serial of accompanying components to perform. Thereby in a system, it may include the elements of micro electromechanical system (MEMS), such as a micropump, a plurality of microvalves, an infrastructure of microchannels, a flow amount detector, microflow switches, and a pressure differential actuator etc. The failure or defect of any element will cause the failure of the entire reaction process. Therefore, the manufacture difficulty is relatively high.
Furthermore, it requires more peripheral supporting electromechanical facilities, and such a requirement is a deviation from the design principle of an on-site, disposable and fast biomedical test kit of microfluidic chips. It is therefore necessary to develop a flow order control device which does not use any power source, movable valves, and peripheral supporting electromechanical facilities to overcome the aforementioned disadvantages.
The literature survey shows that very few elements can provide the high level flow order control function. Most of prior arts focus on changing the microfluidic direction. In 1992, Doring et. al. (Proc. IEEE Micro Electro Mechanical System Workshop, 1992) used the direction that drives the deformation of the hanging arm via thermal expansion to switch the moving fluid direction. The moving fluid would be guided along the tail of the hanging arm into one of the two outlet chambers because of the Coanda effect. This is shown in FIG. 1.
Handique et. al. (US. Patent Publication 2002/0,142,471) disclosed a method of using gas actuators to provide pressure to the moving fluid in order to generate driving force. Valves are placed inbetween two gas actuators and used to separate the gas actuators. When multiple actuators are used, an infrastructure of microchannels is constructed. Ramsey (US. Patent Publication 2003/0,150,733) disclosed a method of using electro osmotic flow or capillary electrophoresis to drive DNA, and then using the voltage change to guide the separated DNA into different channels.
Prior art related to flow order control devices are numerous. However, most of them require not only very complicate chip fabrication process but also more peripheral supporting electromechanical facilities. It is important that such a flow order control device should be low in energy-consumption, low in manufacturing cost and free-of-pollution.